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Tellman IV was an icy mining world[4][43] within the Outworlds Alliance when Operation UNION HOLD began in 2581. After the major Periphery states rejected the Pollux Proclamation in 2575, the Star League began planning for the forced incorporation of all of the Periphery nations into the Star League. Operation UNION HOLD was the name given to the invasion of the Outworlds Alliance, which saw two corps of Star League Defense Force troops and a mixed brigade of DCMS forces begin systematically occupying Alliance worlds. Tellman IV escaped the attentions of the the Star League and Combine forces - collectively referred to as the Outworlds Alliance Task Force - until September 2583, when it became the site of one of the most important battles in the course of the five-year invasion of the Alliance.[4]

In July of 2853, the Chairman of the Outworlds Alliance Militia, Welkens Nordd, had received a vital piece of intelligence; the operational timetable for the Star League forces.[4] The commander of the Outworlds Alliance Task Force, GeneralAmos Forlough, had begun a campaign to weaken the will and ability of the Alliance population to fight by systematically targetting towns, cities and industrial sites on worlds across the Alliance. By the time Nordd received Forlough's timetable, the SLDF forces had already raided Dindatari, Mitchella, Morthac, Quatre Belle and Quiberas since the beginning of 2853, and various other Alliance worlds including the important industrial world of Cerberus were under Star League or Draconis Combine occupation or the subject of ongoing battles and guerilla warfare.[44][45] Access to the operational timetable for the Outworlds Alliance Task Force gave Nordd a chance at stopping Forlough's rampage through the Alliance.[4]

Forlough responded to the departure of the Pitcairn Legion forces from Lushann by reinforcing the SLDF attacks on Banori and Loparri in August but didn't encounter the Legion as expected. The next action on the SLDF timetable was the attack on Tellman IV, for which Forlough tasked and led a mixed division of troops consisting of the 40th Brigade, 43rd Brigade and 45th Brigade, all drawn from V Corps. As with previous attacks on Alliance worlds, scout forces arrived on Tellman IV in mid-September ahead of the main force, tasked with identifying and preparing a suitable landing zone for the bulk of the SLDF forces.
What the V Corps scout forces failed to detect was that they were under constant observation by scouts from Pitcairn's assembled force, who used their observations to position the entire Alliance force ready for the SLDF landing. [4]

Forlough's DropShips landed on the 17th of September and began setting up a temporary encampment while a heavy scout force was sent out. This was the trigger for Pitcairn's ambush; within 20 minutes, the SLDF scout 'Mechs had been destroyed, and Pitcairn's forces were engaged in battle with the main SLDF force inside the SLDF landing zone.[4]

Pitcairn's forces were attempting to destroy tanks and 'Mechs before their crews could finish preparing them for battle, but the battle itself rapidly became a virtual firestorm as three years of Alliance rage and frustration was released against the Star League forces. With the cry "Cerberus Lives!" audible above the noise of battle, the Alliance forces battled the SLDF troops until after nightfall; the battlefield was a swirling maelstrom of chaos which only increased as frantic SLDF DropShip crews began firing at real and imagined targets, and escalated further still as several DropShips lifted off, damaging Alliance and V Corps forces alike with their drive plumes.[4]

By the time Forlough ordered a general retreat from Tellman IV, the battle had inflicted a heavy cost on the assembled Alliance forces; more than a hundred Alliance 'Mechs had been lost, and almost another hundred had been badly damaged, losses that could partially be recouped from salvaged SLDF equipment but which would take time to recover from. The material losses for the SLDF forces had been greater, though; the Alliance "Day of Vengeance" had cost V Corps more than 200 'Mechs, 200 vehicles, four DropShips and almost 2,000 men - 800 of whom had been captured and would end up in Alliance POW camps. In a single day-long battle V Corps had lost a third of it's effective combat strength and Forlough's raids on the Alliance had been checked.[4][47]

AFFS forces launched a heavy raid on Tellman IV between the 21st and 28th of June 3072, attempting to find what they believed to be Word of Blake command centers on the planet. Despite the quantity of AFFS forces committed to the raid, the Outworlds Alliance and Clan Snow Raven forces defending Tellman IV were able to quickly defeat and capture the AFFS troops.[48][49]